The U.S. Department of Veterans Affairs withheld data showing links between Gulf War veterans’ illnesses and toxic environmental hazards they were exposed to such as burn pits in Iraq and Afghanistan, a whistleblower told a House hearing on Wednesday.

Charging the accusations was Dr. Steven Coughlin, who worked as a senior epidemiologist at the VA’s Office of Public Health for over four years until December when he resigned “because of serious ethical concerns.”

“If the studies produce results that do not support Office of Public Health’s unwritten policy, they do not release them,” Coughlin told the House Subcommittee on Oversight and Investigations.

“This applies to data regarding adverse health consequences of environmental exposures, such as burn pits in Iraq and Afghanistan, and toxic exposures in the Gulf War. On the rare occasions when embarrassing study results are released, data are manipulated to make them unintelligible,” he said.

On research Coughlin was involved with that looked at data of veterans’ exposure to pesticides and oil well fires among other things, he said that “The Office of Public Health has not released these data, or even the fact that this important information on Gulf War veterans exists.”

“Anything that supports the position that Gulf War illness is a neurological condition is unlikely to ever be published.”

In 2010, Coughlin participated in a study of recent veterans of Iraq and Afghanistan that linked exposure to burn pits to greater incidences of asthma or bronchitis. His request to see their medical records was denied, Coughlin said, and the results of the study were never published.

“I was very concerned they were withholding data or misleading people,” he told USA TODAY. “I don’t want to speculate about why.”

Coughlin told Fox News in an interview, “I was told two or three times in the second half of 2012 by my immediate supervisor not to look at data.” When he said he didn’t want to work on the project with those limitations, Coughlin said that his supervisor threatened him.

If Coughlin’s allegations prove true, a leading veterans’ advocate told the Project on Government Oversight (POGO), the conduct by the VA “would be a total breach of trust with all veterans and their families.”